There is nothing new about police outsourcing, though the headlines would have you think otherwise. The contracts that West Midlands and Surrey police forces want to sign are extremely similar to those signed by Cleveland police authority and Steria, in July 2011.

Other contracts for police services abound. Since 2003, G4S has managed 500 police cells in Lancashire, South Wales and Staffordshire, fingerprinting and searching suspects, completing witness statements, and preparing and managing bail.

Chief constables point out that they can save money and improve performance. The trend towards higher value contracts covering a wider scope of police work still merits attention, however. To a degree, the debate is pragmatic. Do the potential benefits of contracting with specialist firms outweigh the reduced responsiveness that occurs? If you manage your finance director, for example, you can tell them to process 100 more payments this week but if you have a contract that says up to 800 payments per week and you have already done 780 then you can't.

Private sector companies struggle with exactly this question. Sainsbury's brought its IT function back in-house in 2005 after outsourced stock-ordering systems had failed to get stock on to supermarket shelves. It also ended a separate outsourcing contract with Accenture, which had been providing and supporting most of Sainsbury's IT systems (with the notable exception of the automated stock-ordering system).

In 2009, after outsourcing the manufacture of its aircraft parts, Boeing spent about $1bn to take back the fuselage manufacturing plant of Vought Aircraft Industries. Generally, the closer that outsourcing gets to a company's "core business", the harder it gets to transfer the costs of underperformance.

Outsourcing judgments are harder to make in the public sector, as Testing New Commissioning Models, an Institute for Government report published later this week on government outsourcing, demonstrates.

Why is this? First, government contracts must respect the political context. Will long contracts such as the proposed 15-year arrangement in the West Midlands and Surrey be sufficiently flexible, for example, to allow police and crime commissioners, who will be elected in November 2012, to later change strategic direction? And are there robust measures to ensure continuity of service?

Second, government should not outsource services when it doesn't understand the costs of delivery or what good performance looks like. In too many cases, such information is missing, as the National Audit Office last week demonstrated. Its shared services report showed that a number of Whitehall departments that share back office services could not even say whether this is reducing overall costs, let alone its impact on effectiveness.

Third, government organisations must invest in building the skills and evidence base needed to contract effectively. Given the relative inexperience with outsourcing and historic neglect of anything in policing that is not to do with "bobbies on the beat", it is highly likely that the skills issue requires attention.

In this context, it is vital that West Midlands and Surrey police assess their ability to successfully manage their contracts. They will do everyone in public services a favour if they lead the way and evaluate whether the contracts they are putting in place actually work.

• Tom Gash is programme director at the Institute for Government and co-author of Testing New Commissioning Models, a guide to government outsourcing

• This article was amended on 16 March 2012. The original said that difficulties experienced by Sainsbury's under its outsourced IT contract with Accenture included failures to get stock on to supermarket shelves. In fact, the stock-ordering systems were outside the Accenture contract. They were provided by a different company.

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